Light emitting device and system providing white light with various color temperatures

ABSTRACT

In a light emitting device and system providing white light with various color temperatures are provided, a light emitting device includes a light emitting element (LED) that is operated by a driving bias and emits first light, and a phosphor layer including a phosphor that partially wavelength-converts first light and emits second light, thereby emitting white light using the first light and the second light, wherein the phosphor has a maximum conversion efficiency at a first level of the driving bias, and the LED has a maximum conversion efficiency at a second level of the driving bias, the first level being different from the first level.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 12/584,513, filed on Sep. 8, 2008, which claimspriority from Korean Patent Application No. 10-2008-0089439 filed onSep. 10, 2008 in the Korean Intellectual Property Office, the entirecontents of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention relate to a light emitting deviceand system providing white light with various color temperatures.

2. Description of the Related Art

Light emitting elements, such as light emitting diodes (LEDs), emitlight as a result of the induced recombination of electrons and holes.LEDs consume a reduced amount of power and enjoy relatively longlifespan as compared to conventional incandescent light bulbs or otherlight sources. Additionally, LEDs can be highly integrated and can beplaced in a narrow spaces. Further, LEDs are resistant to vibration.

A light emitting device is capable of generating light of variouswavelengths according to the manner in which it is manufactured. Forexample, light emitting devices can be configured to generate bluelight, ultraviolet (UV) light, white light, or the like.

An example method of manufacturing a white light emitting device capableof generating white light will now be described. That is to say, a whitelight emitting device capable of generating bluish white light can bemanufactured by coating a yellow phosphor material on a bluish lightemitting element (LED) that emits blue light. Alternatively, the whitelight emitting device capable of generating reddish white light can bemanufactured by coating a yellow phosphor material and red phosphormaterial on the bluish LED.

The above-example white light emitting devices, however, are commonlydeveloped to be configured using a phosphor coating technique thatmaximizes luminescence efficiency at a fixed color temperature, that is,a temperature of bluish white or reddish white. As a result, a devicethat outputs white light with various color temperatures cannot beimplemented using a single white light emitting device.

SUMMARY

Embodiments of the present specification provide a light emitting devicecapable of providing white light with various color temperatures.

Embodiments of the present specification also provide a light emittingsystem capable of providing white light with various color temperatures.

The above and other objects will be described in or be apparent from thefollowing description of the preferred embodiments.

According to an aspect, there is provided a light emitting deviceincluding a light emitting element (LED) that is operated by a drivingbias and emits first light, and a phosphor layer including a phosphorthat partially wavelength-converts first light and emits second light,thereby emitting white light using the first light and the second light,wherein the phosphor has a maximum conversion efficiency at a firstlevel of the driving bias, and the LED has a maximum conversionefficiency at a second level of the driving bias, the first level beingdifferent from the first level.

Here, the color temperature of the white light can be varied byadjusting the level of the driving bias. In detail, the second light canhave a dominant wavelength at the first level of the driving bias in thewhite light, and the first light can have a dominant wavelength at thesecond level of the driving bias in the white light.

In an exemplary embodiment, the LED may be a blue LED that emits bluelight, and the phosphor may include a red phosphor that partiallywavelength-converts the blue light and emits red light, a yellowphosphor that partially wavelength-converts the blue light and emitsyellow light, or a green phosphor that partially wavelength-converts theblue light and emits green light. In this case, reddish white light isgenerated at the first level of the driving bias, and bluish white lightis generated at the second level of the driving bias.

In another exemplary embodiment, the LED may be a UV LED that emits a UVlight, the phosphor may include a red phosphor that partiallywavelength-converts the UV light and emits red light, a green phosphorthat partially wavelength-converts the UV light and emits green light,and a blue phosphor that partially wavelength-converts the UV light andemits blue light. Here, the blue phosphor has the maximum conversionefficiency at the second level of the driving bias.

According to another aspect, there is provided a light emitting devicecomprising a light emitting element (LED) that is operated by a drivingbias and emits first light, a first phosphor that partiallywavelength-converts the first light and emits second light, and secondphosphor that partially wavelength-converts the first light and emitsthird light, thereby emitting white light using the first light, thesecond light and the third light, wherein the first phosphor has amaximum conversion efficiency at a first level of the driving bias, andthe second phosphor has a maximum conversion efficiency at a secondlevel of the driving bias, the first level being different from thefirst level.

Here, the color temperature of the white light may be varied byadjusting the level of the driving bias. In detail, the second light hasa dominant wavelength at the first level of the driving bias in thewhite light, and the third light has a dominant wavelength at the secondlevel of the driving bias in the white light.

In an exemplary embodiment, the LED may be a UV LED that emits a UVlight, the first phosphor may include a red phosphor that partiallywavelength-converts the blue light and emits red light, and the secondphosphor is a blue phosphor that partially wavelength-converts the UVlight and emits blue light.

According to still another aspect, there is provided a light emittingdevice comprising a blue light emitting element (LED) that is operatedby a driving bias and emits blue light, and a red phosphor thatpartially wavelength-converts the blue light and emits red light,thereby emitting white light using the blue light and the red light,wherein reddish white light or bluish white light is generated byadjusting the level of the driving bias.

Here, reddish white light may be generated at a first level of thedriving bias, and bluish white light may be generated at a second levelof the driving bias, the first level being different from the firstlevel. The second level is preferably higher than the first level.

In addition, the red phosphor may have a maximum conversion efficiencyat the first level of the driving bias, and the blue phosphor may have amaximum conversion efficiency at the second level of the driving bias.

The light emitting device may further include a yellow phosphor thatpartially wavelength-converts the blue light and emits yellow light, ora green phosphor that partially wavelength-converts the blue light andemits green light.

Here, the driving bias can be DC power.

According to a further aspect, there is provided a light emitting systemincluding the light emitting device and a sensor that senses user's bodytemperature, wherein the level of the driving bias is controlled by thesensor.

According to still further aspect, there is provided a light emittingsystem comprising the light emitting device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail preferred embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view of a light emitting device according toa first embodiment of the present invention;

FIG. 2, and FIGS. 3A through 3C are detailed diagrams illustratingexemplary connection between a package body and an emitter;

FIG. 4 is a cross-sectional view of a light emitting device according toa second embodiment of the present invention;

FIG. 5 is a cross-sectional view of a light emitting device according toa third embodiment of the present invention;

FIG. 6A is a cross-sectional view of a light emitting device accordingto a fourth embodiment of the present invention;

FIG. 6B is a cross-sectional view of a light emitting device accordingto a fifth embodiment of the present invention;

FIG. 7 is a diagram illustrating effects of light emitting devicesaccording to embodiments of the present invention;

FIG. 8 is a diagram illustrating a light emitting system according to afirst embodiment of the present invention;

FIG. 9 is a diagram illustrating a light emitting system according to asecond embodiment of the present invention; and

FIGS. 10 through 13 are diagrams illustrating light emitting systemsaccording to third through sixth embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will now be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in different forms and should not be construed aslimited to the embodiments set forth herein. Like numbers refer to likeelements throughout the specification.

It will be understood that, although the terms first, second, etc. areused herein to describe various elements, these elements should not belimited by these terms. These terms are used to distinguish one elementfrom another. For example, a first element could be termed a secondelement, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being “on”or “connected” or “coupled” to another element, it can be directly on orconnected or coupled to the other element or intervening elements can bepresent. In contrast, when an element is referred to as being “directlyon” or “directly connected” or “directly coupled” to another element,there are no intervening elements present. Other words used to describethe relationship between elements should be interpreted in a likefashion (e.g., “between” versus “directly between,” “adjacent” versus“directly adjacent,” etc.). When an element is referred to herein asbeing “over” another element, it can be over or under the other element,and either directly coupled to the other element, or interveningelements may be present, or the elements may be spaced apart by a voidor gap.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of the invention. As usedherein, the singular forms “a,” “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

FIG. 1 is a cross-sectional view of a light emitting device according toa first embodiment of the present invention, in which only main partsare simplified or exaggerated and shown. FIG. 2, and FIGS. 3A through 3Care detailed diagrams illustrating exemplary connection between apackage body and an emitter. FIG. 7 is a diagram illustrating effects oflight emitting devices according to embodiments of the presentinvention.

Referring first to FIG. 1, a light emitting device 1 according to afirst embodiment includes a package body 10, a light emitting diode(LED) 20, a submount 30, a transparent resin layer 50, and a phosphorlayer 60.

The LED 20 may be disposed on the package body 10. In detail, thepackage body 10 may incorporate a slot 12, and the LED 20 may bedisposed within the slot 12 or may be otherwise connected to the slot12. In particular, the slot 12 may have sloping sidewalls. Lightgenerated from the LED 20 may be reflected at the sidewalls to thentravel outward direction.

While FIG. 1 illustrates that the LED 20 is connected to the submount 30and the LED 20 connected to the submount 30 is disposed in the slot 12of the package body 10, the connection relationship is not limited tothe illustrated example. For example, the LED 20 may be directly mountedon the package body 10 without using the submount 30.

Meanwhile, the package body 10 and the LED 20 may be connected to eachother in various manners. For example, the package body 10 and the LED20 may be connected to each other in such manners as shown and describedbelow in connection with FIGS. 2 and 3A through 3C, and in other ways.

Referring to FIGS. 2 and 3A, the LED 20 may be an LED (Light EmittingDiode), and may be mounted on the submount 30. The LED 20 can include afirst conductive layer of a first conductivity type (e.g., n type), asecond conductive layer of a second conductivity type (e.g., p type), alight emitting layer disposed between the first conductive layer and thesecond conductive layer, a first electrode connected to the firstconductive layer, and a second electrode connected to the secondconductive layer. When a forward driving bias is applied to the LED 20,light is generated by recombination of carriers (i.e., electrons) of thefirst conductive layer and carriers (i.e., holes) of the secondconductive layer in the light emitting layer. The first conductivelayer, the second conductive layer, and the light emitting layer of theLED can be represented by the following Chemical FormulaIn_(x)Al_(y)Ga_((1-x-y))N (0≦x≦1, 0≦y≦1).

The LED 20 may be operated by applying a driving bias between the firstelectrode and the second electrode. The driving bias corresponds to theabsolute value of a difference between a first bias applied to the firstelectrode and a second bias applied to the second electrode. Here, thedriving bias may be DC power.

Meanwhile, the LED 20 of a flip chip type LED is illustrated by way ofexample, but the present invention is not limited thereto. For example,the LED 20 may be a lateral type LED or a vertical type LED. In the flipchip type LED, a first electrode and a second electrode are oriented ina downward direction. In the lateral type LED, a first electrode and asecond electrode are oriented in an upward direction. In the verticaltype LED, one of first and second electrodes is oriented in an upwarddirection, while the other of the first and second electrodes isoriented in a downward direction.

In addition, while the LED 20 of a top view type is illustrated in FIG.2, meaning that light is outwardly emitted from a top of the device,embodiments of the present invention are not limited thereto. Forexample, the LED 20 may be of a side view type. In a case where the LED20 is of a top view type, it can generally be square in shape having asize of at least 1 mm×1 mm. In addition, the top view type LED 20radiates light directly on an object, and is typically used for alighting device, a display device, and so on. By comparison, a side viewtype LED is generally rectangular in shape, having a size of at least 70μm×300 μm, (e.g., 150 μm×400 μm), and is variable in size according tothe kind of device applied. The side view type LED is usually used formobile equipment, such as a mobile phone, an MP3 player, a navigationdevice, etc., a display device, or the like. The top view type LED andthe side view type LED are substantially the same in terms of theirconfigurations and operations, except for their respective sizes andshapes.

In other embodiments, the LED 20 may be a blue LED 20 that emits bluelight, that is, light of a blue emission wavelength, or, in otherembodiments, a UV LED 20 that emits UV light.

The LED 20 is disposed within the slot 12 of the package body 10. Theslot 12 is larger than the LED 20. The size of the slot 12 may bedetermined in consideration of the extent in which the light generatedfrom the LED 20 is reflected at sidewalls 12 a of the slot 12, the angleof reflection, the type of transparent resin layer 50 filling the slot12, or the type of phosphor layer 60. The LED 20 is preferably placed ata middle region of the slot 12. When distances between the LED 20 andeach of the sidewalls 12 a are substantially the same, nonuniformity inthe chromaticity diagram can be avoided.

The package body 10 can be formed, for example, of an organic materialhaving excellent light transmittance, such as a silicon resin, an epoxyresin, an acryl resin, a glass resin, a fluorine resin, or an imideresin, or an inorganic material having excellent light transmittance,such as glass, or silica gel. In order to prevent a resin material frombecoming melted due to heat generated during manufacturing, a thermallyreinforced resin can be used. In order to alleviate inherent thermalstress in a resin, a variety of fillers including aluminum nitride,aluminum oxide, and composite materials thereof may also be added.However, materials of the package body 10 are not limited to resinmaterials. For example, the package body 10 may be formed of a metallicor ceramic material in part (e.g., the sidewalls 12 a), or entirely. Ifthe package body 10 is entirely formed of, for example, a metallicmaterial, the heat generated from the LED 20 is easily transferredexternally.

FIG. 3A shows a case in which the package body 10 is entirely formed ofa metallic material. As illustrated, the package body 10 furtherincludes leads 14 a and 14 b electrically connected to the LED 20. TheLED 20 is electrically connected to the submount 30, and the submount 30is connected to the leads 14 a and 14 b through wires 16 a and 16 b. Theleads 14 a and 14 b may be formed of a material having a highlythermally conductive material to allow the heat generated from the LED20 to be externally transferred through the leads 14 a and 14 b.

Meanwhile, the light emitting device shown in FIG. 3B is different fromthat shown in FIG. 3A in that the submount 30 is connected to the leads14 a and 14 b through a conductive via 32 provided in the submount 30.The light emitting device shown in FIG. 3C is different from that shownin FIG. 3A in that the submount 30 is connected to the leads 14 a and 14b through interconnections 34 provided on the top, lateral, and rearsurfaces of the submount 30. The light emitting devices shown in FIGS.3B and 3C can provide enhanced device integration, since wires are notemployed.

As described above in connection with FIGS. 2 and 3A through 3C,embodiments of the present invention can be applied to various types oflight emitting devices.

Referring back to FIG. 1, a transparent resin layer 50 may be coated onthe LED 20. In detail, the transparent resin layer 50 may fill at leastsome of the slot 12. For example, as shown in FIG. 1, the transparentresin layer 50 does not completely fill the slot 12 but rather fillsapproximately 90% of the slot 12.

The transparent resin layer 50 can be formed of any material that can beused to fill the slot 12 of the package body 10, but is not particularlylimited. Example materials of the transparent resin layer 50 that can beemployed include resins, such as epoxy resin, silicon resin, hardenedsilicon resin, denatured silicon resin, urethane resin, ocetane resin,acryl resin, polycarbonate resin, polyimide resin, or the like.

The phosphor layer 60 can be formed on the transparent resin layer 50.In detail, the phosphor layer 60 can be a combination of a transparentresin 62 and a phosphor 64, but not limited thereto. That is to say, thephosphor layer 60 may include only the phosphor 64 material, without thetransparent resin 62 material.

The phosphor 64 will now be described in more detail. The phosphor 64 isa material that absorbs the light emitted from the LED 20 andwavelength-converts the same into light of a different wavelength. Thatis to say, the phosphor 64 is a material, which absorbs light based onprimary luminescence of the LED 20 and emits light by secondaryluminescence.

The phosphor 64 allows the resulting light emitting device to rendervarious colors. For example, rendering white light can be performed inthe following manner. If the LED 20 emits blue light, i.e., light of ablue wavelength, which is referred to as a blue LED, the phosphor layer60 partially wavelength-converts the blue light containing a yellowphosphor that emits yellow light, and a red phosphor that emits redlight. Alternatively, the phosphor layer 60 may partiallywavelength-convert to produce a green phosphor that emits green light.Further, the phosphor layer 60 may partially wavelength-convert toproduce a red phosphor that emits red light. That is to say, in a casewhere the LED 20 is a blue LED, primary light emitted from the LED 20and secondary light emitted from the phosphor are combined together tooutput a combined white light.

In a case where the LED 20 emits UV light of a UV wavelength, which isreferred to as a UV LED, the phosphor layer 60 may include a redphosphor, a green phosphor, and a blue phosphor (i.e., RGB).

The phosphor 64 is preferably at least one selected from anitride-/oxynitride-based phosphor, mainly activated by lanthanoids suchas Eu and Ce; an alkaline earth halogen apatite phosphor, mainlyactivated by lanthanoids such as Eu or by transition metal elements suchas Mn; an alkaline earth metal borate halogen phosphor; an alkalineearth metal aluminate phosphor; an alkaline earth sulfide phosphor; arare earth aluminate phosphor, mainly activated by lanthanoids such asCe; an alkaline earth silicate phosphor; an alkaline earth thiogallatephosphor, an alkaline earth silicon nitride phosphor; a germinatephosphor; and an organic and an organic complexes, mainly activated bylanthanoids such as Eu. As specific examples, the phosphors shown belowcan be used but it is not limited thereto.

Examples of the nitride-based phosphor that is mainly activated withlanthanoid elements such as Eu and Ce include M₂Si₅N₈:Eu, M₂Si₅N₈:Eu,MSi₇N₁₀:Eu, M_(1.8)Si₅O_(0.2)N₈:Eu, M_(0.9)Si₇O₉:Eu (wherein Mrepresents at least one element selected from among Sr, Ca, Ba, Mg andZn).

Examples of the oxynitride phosphor that is mainly activated withlanthanoid elements such as Eu and Ce include MSi₂O₂N₂:Eu (wherein Mrepresents at least one element selected from among Sr, Ca, Ba, Mg andZn).

Examples of the alkaline earth halogen apatite phosphor that is mainlyactivated with lanthanoid elements such as Eu, or with transition metalelements such as Mn include M₅(PO₄)₃X:R (wherein M represents at leastone element selected from among Sr, Ca, Ba, Mg and Zn, X represents atleast one element selected from among F, Cl, Br, and I, and R representsEu or Mn, or Eu and Mn.

Examples of the alkaline earth metal borate halogen phosphor includeM₂B₅O₉X:R (wherein M represents at least one element selected from amongSr, Ca, Ba, Mg and Zn, X represents at least one element selected fromamong F, Cl, Br, and I, and R represents Eu or Mn, or Eu and Mn).

Examples of the alkaline earth metal aluminate phosphor includeSrAl₂O₄:R, Sr₄Al₁₄O₂₅:R, CaAl₂O₄:R, BaMg₂Al₁₆O₂₇:R, BaMg₂Al₁₆O₁₂:R,BaMgAl₁₀O₁₇:R(R represents Eu or Mn, or Eu and Mn).

Examples of the alkaline earth sulfide phosphor include La₂O₂S:Eu,Y₂O₂S:Eu, Gd₂O₂S:Eu.

Examples of the rare earth aluminate phosphor that is mainly activatedwith lanthanoid elements such as Ce include YAG-based phosphorsrepresented by the formulas: Y₃Al₅O₁₂:Ce, (Y_(0.8)Gd_(0.2))₃Al₅O₁₂:Ce,Y₃(Al_(0.8)Ga_(0.2))₅O₁₂:Ce, and (Y, Gd)₃ (Al, Ga)₅O₁₂. Examples of therare earth aluminate phosphor also include Tb₃Al₅O₁₂:Ce, Lu₃Al₅O₁₂:Ce inwhich portion or all of Y is substituted with Tb or Lu.

Examples of the alkaline earth silicate phosphor include silicates suchas (SrBa)₂SiO₄:Eu.

Examples of other phosphors include ZnS:Eu, Zn₂GeO₄:Mn, MGa₂S₄:Eu(wherein M represents at least one element selected from among Sr, Ca,Ba, Mg and Zn, and X represents at least one element selected from amongF, Cl, Br and I).

If necessary, the phosphors described above can contain at least oneelement selected from among Tb, Cu, Ag, Au, Cr, Nd, Dy, Co, Ni and Ti,in place of Eu, or in addition to Eu.

It is possible to use a phosphor which is other than the phosphordescribed above and has the same performance and effect as those of thephosphors.

The light emitting device 1 according to the first embodiment of thepresent invention can operate as follows. In the following description,the operation of the light emitting device 1 will be described withreference to FIG. 3A. Embodiments of the present invention can equallybe applied to other types of light emitting devices, such as those shownin FIGS. 3B and 3C.

Referring to FIGS. 1 and 3A, when a first bias (e.g., V−, I−, or ground)is externally applied to the lead 14 a, the first bias is transmitted tothe first electrode of the LED 20 through the wire 16 a and the submount30. When a second bias (e.g., V+ or I+) is externally applied to thelead 14 b, the second bias is transmitted to the second electrode of theLED 20 through the wire 16 b and the submount 30. That is to say, adriving bias corresponding to the absolute value of a difference betweenthe DC power and the second bias is applied to the LED 20. Then, thedriving bias actuates the LED 20 to generate light. In a case where theLED 20 is a blue LED, blue light is generated. In a case where the LED20 is a UV LED, UV light is generated.

The light generated from the LED 20 is partially wavelength-converted bythe phosphor material in the phosphor layer 60. For example, the yellowphosphor is converted into yellow light, the green phosphor is convertedinto green light, and the red phosphor is converted into red light.

The light generated from the LED 20 and the light that iswavelength-converted in the phosphor layer 60 are mixed and outputtogether. In such a manner, the light emitting device 1 emits whitelight.

The light emitting device 1 according to the first embodiment of thepresent invention can vary color temperatures of white light byadjusting the level of the driving bias.

First, when the driving bias is at a first level, the white light thatis generated may be reddish white light, and when the driving bias is ata second level that is different from the first level, the white lightmay be bluish white light. Here, the second level may be higher than thefirst level. In other embodiments, the second level may be lower thanthe first level.

Referring to FIG. 7, the x axis indicates the driving bias, and the yaxis indicates the standardized intensity of the emitted light. FIG. 7shows that standardized intensities of red light, green light, and bluelight according to varying driving biases in cases where a UV LED isused as the LED 20, a red phosphor is used as the phosphor in thephosphor layer 60, and a green phosphor and a blue phosphor are used. InFIG. 7, reference symbol ‘a’ indicates the red light, ‘b’ indicates thegreen light, and ‘c’ indicates the blue light, respectively.

In plot ‘a’ corresponding to red light, the intensity of red light isnearly saturated even when the driving bias is not so high (e.g., 500mA). That is to say, there is no significant intensity difference in theintensity of the generated red light at driving biases between about 500mA and 900 mA. In detail, when the driving bias is 500 mA, the redphosphor can be said to have a maximum conversion efficiency. Themaximum conversion efficiency refers to the extent in which eachphosphor receives light from a LED and maximally converts the receivedlight. For example, assuming that the light quantity of approximately100 is generated from a LED and the phosphor is capable of maximallyconverting the light quantity of approximately 30, the maximumconversion efficiency is 30%. The maximum conversion efficiency is adriving level at which the intensity does not increase any further.

On the other hand, in plot ‘c’ corresponding to blue light, there is asignificant intensity difference between driving biases 500 mA and 900mA. That is to say, the intensity of blue light is not saturated untilthe driving bias is 900 mA or higher. If the intensity of blue light issaturated at the driving bias of 900 mA, the blue phosphor has themaximum conversion efficiency at a value of the driving bias of 900 mA.

It can be understood from FIG. 7 that each respective phosphor materialhas a maximum conversion efficiency at a specific driving bias. In otherwords, the driving bias level at which the red phosphor, i.e. plot ‘a’,demonstrates the maximum conversion efficiency may be different from thedriving bias level at which the blue phosphor, i.e. plot ‘c’,demonstrates the maximum conversion efficiency.

Referring back to FIGS. 1 and 3A, the configuration of the lightemitting device 1 according to the first embodiment of the presentinvention will now be described in consideration of the aforementionedoperational characteristics.

The light emitting device 1 includes the LED 20 that is operated by adriving bias and emits first light, and the phosphor layer 60 includingthe phosphor 64 that partially wavelength-converts the first light andemits second light. Thus, the light emitting device 1 emits white lightusing the first light and the second light. The phosphor 64 has themaximum conversion efficiency at a first level of the driving bias. TheLED 20 has the maximum conversion efficiency at a second level of thedriving bias, which is different from the first level.

In a first example, it is assumed that the LED 20 is a blue LED and thephosphor 64 is a red phosphor or a green phosphor (or a yellowphosphor).

For example, the blue LED may have the maximum conversion efficiency atapproximately 900 mA, and the red phosphor may have the maximumconversion efficiency at approximately 500 mA.

Since the blue LED cannot maximize its luminescence efficiency at 500mA, blue light is not emitted to the maximum efficiency, while the redphosphor is capable of converting the emitted blue light into red lightto maximum efficiency. That is, red light is dominantly present in thewhite light that has the light emitted from the blue LED and the lightemitted from the red phosphor mixed together. Thus, the resulting whitelight emitted from the light emitting device 1 is reddish white.

On the other hand, since the blue LED has the maximum luminescenceefficiency at approximately 900 mA, it emits blue light to the maximumefficiency, and the red phosphor is capable of converting as much lightas converted at 500 mA. That is, blue light is dominantly present in thewhite light having the light emitted from the blue LED and the lightemitted from the red phosphor mixed together. Thus, the white lightemitted from the light emitting device 1 is bluish white.

In a second example, it is assumed that the LED 20 is a UV LED and thephosphor 64 is a red phosphor, a blue phosphor, or a green phosphor (ora yellow phosphor).

For example, the UV LED may have the maximum conversion efficiency atapproximately 900 mA, the red phosphor may have the maximum conversionefficiency at approximately 500 mA, and the blue phosphor may have themaximum conversion efficiency at approximately 900 mA, respectively.

Since the UV LED cannot maximize its luminescence efficiency at 500 mA,UV light is not emitted to the maximum, while the red phosphor iscapable of converting the emitted UV light into red light to themaximum. In addition, the blue phosphor is capable of converting theemitted UV light into blue light, but not to the maximum. That is, redlight is dominantly present in the white light having the light emittedfrom the blue LED and the light emitted from the red phosphor mixedtogether. Thus, the white light emitted from the light emitting device 1is reddish white.

On the other hand, since the UV LED has the maximum luminescenceefficiency at approximately 900 mA, it emits UV light to the maximum,and the red phosphor is capable of converting as much light as convertedat 500 mA. In addition, the blue phosphor is capable of converting asmuch as the emitted UV light as possible into blue light. That is, bluelight is dominantly present in the white light having the light emittedfrom the red phosphor and the light emitted from the blue phosphor mixedtogether. Thus, the white light emitted from the light emitting device 1is bluish white.

The light emitting device 1 according to the first embodiment of thepresent invention includes a LED that is operated by a driving bias andemits first light, a first phosphor that partially wavelength-convertsthe first light and emits second light, and a second phosphor thatpartially wavelength-converts the first light and emits third light,thereby emitting white light using the first light, the second light andthe third light. The first phosphor has the maximum conversionefficiency at a first level of the driving bias, and the second phosphorhas the maximum conversion efficiency at a second level of the drivingbias, the first level being different from the first level.

Here, the LED may be a UV LED, the first phosphor may be a red phosphor,and a second phosphor may be a blue phosphor. In order to produce whitelight, the LED may further include a green phosphor (or a yellowphosphor).

It is assumed, in one example, that the UV LED has the maximumconversion efficiency at approximately 1000 mA, the red phosphor has themaximum conversion efficiency at approximately 500 mA, and the bluephosphor has the maximum conversion efficiency at approximately 900 mA.Then, white light emitted from the light emitting device 1 becomesreddish at 500 mA, and bluish at 900 mA.

As described above, the color temperature of the white light may bevaried by adjusting the level of the driving bias. At the first level ofthe driving bias (approximately 500 mA in the above example), the secondlight (i.e., red light) is present more dominantly than the first light(i.e., blue light) in the white light, and the white light becomesreddish. In addition, at the second level of the driving bias(approximately 900 mA in the above example), the first light (i.e., bluelight) is present more dominantly than the second light (i.e., redlight) in the white light, and the white light becomes bluish.

When the LED 20 has the maximum luminescence efficiency at the secondlevel, bluish white light is emitted from the light emitting device 1 atapproximately maximum efficiency, but reddish white light is not emittedwith the maximum efficiency. The light emitting device 1 according tothe first embodiment of the present invention is advantageous in that itcan generate bluish white light and reddish white light, even if thereis a small reduction in luminescence efficiency. In other words, whitelight having various color temperatures can be generated from a singleunit of the light emitting device 1.

FIGS. 4 through 6B are cross-sectional views of light emitting devicesaccording to second through fifth embodiments of the present invention.The operating principles of the light emitting devices according tosecond through fifth embodiments of the present invention aresubstantially the same as those of the first embodiment of the presentinvention. That is to say, the light emitting devices according tosecond through fifth embodiments of the present invention can varyaccording to color temperatures of white light by adjusting the level ofa driving bias.

Referring first to FIG. 4, the light emitting device 2 according to thesecond embodiment is different from the light emitting device 1according to the first embodiment in that it has a filter 80 formed on aphosphor layer 60. The filter 80 absorbs light of a particularwavelength. For example, the filter 80 can be configured to absorb thelight primarily emitted from the LED 20, and to not absorb the lightsecondarily emitted from the phosphor layer 60. The filter 80 may beformed of a material capable of dispersing heat while absorbing light ofa particular wavelength. Usable examples of the filter 80 include aninorganic dye or an organic dye.

In particular, when the LED 20 is a UV emitter, a UV filter can be usedas the filter 80 since excessive UV light may be harmful to human body.

Referring to FIG. 5, the light emitting device 3 according to the thirdembodiment is different from the light emitting device 1 according tothe first embodiment in that it has a phosphor layer 60 shaped of alens. In order to improve light diffusion/extraction characteristics ofthe LED 20, the phosphor layer 60 may have a predetermined curvature.While FIG. 5 shows that the phosphor layer 60 has a shape of a convexlens, it may have a shape of a concave lens.

Referring to FIG. 6A, the light emitting device 4 according to thefourth embodiment is different from the light emitting device 1according to the first embodiment in that it has a transparent resinlayer 50 formed only on the LED 20 and the submount 30 and the phosphorlayer 60 and the phosphor material 64 contained therein is dispersedthroughout the transparent resin layer 50 to fill a slot 12.

Referring to FIG. 6B, the light emitting device 5 according to the fifthembodiment is different from the light emitting device 1 according tothe first embodiment in that it has a phosphor 64 that is conformallyformed on the LED 20 and the submount 30. A transparent resin 62 isformed on the conformal phosphor layer 64.

Hereinafter, light emitting systems manufactured using theabove-described light emitting devices 1 through 4 will be described.For brevity of explanation, embodiments will be described with regard toa light emitting system using the light emitting device 1 according tothe first embodiment of the present invention by way of example, but theinvention is not limited thereto. Rather, it will be apparent to thoseskilled in the art that the light emitting system can optionally beimplemented using the light emitting devices of the second through fifthembodiments described above, and other configurations.

FIG. 8 is a diagram illustrating a light emitting system according to afirst embodiment.

Referring to FIG. 8, the light emitting system according to the firstembodiment includes an LED 1, a bias generator 85, and a sensor 90.

In detail, the LED 1 receives a driving bias from the bias generator 85and generates white light. The bias generator 85 receives a controlsignal from the sensor 90 and controls the level of the driving bias.

In particular, if the level of the driving bias is adjusted by thesensor 90, the color temperatures of white light can be adjusted in tunewith the user's emotion. For example, if the sensor 90 senses the user'sbody temperature, that is, if the sensed user's body temperature isrelatively low, the LED 1 emits reddish white light of a warm colortemperature, while if the sensed user's body temperature is relativelyhigh, the LED 1 emits bluish white light of a cold color temperature.

The sensor 90 may be installed on a door handle or door lock to allowthe user's body temperature to be easily sensed. For example, the sensor90 can sense the user's body temperature using infrared rays. Althoughin the embodiment described above the color temperatures of white lightcan be adjusted according to the user's body temperature, embodiments ofthe present invention are not limited thereby, and other forms ofexternal stimulus can optionally be used to drive the bias generator 85.

FIG. 9 is a diagram illustrating a light emitting system according to asecond embodiment of the present invention.

Referring to FIG. 9, the light emitting system is an exemplary system,e.g., an end product, to which the light emitting device 1 according tothe first embodiment is incorporated. The light emitting system can beapplied to a variety of devices, including an illumination device, adisplay device, a mobile device (e.g., a mobile phone, an MP3 player, anavigation device, etc.), and so on. The light emitting systemillustrated in FIG. 9 is an edge type backlight unit (BLU) used for aliquid crystal display (LCD). Since the LCD is not a self-emittingdevice, a BLU, which is usually provided in rear of an LCD panel, isused as a light source.

Referring to FIG. 9, the BLU includes a light emitting device 1, a lightguiding plate 410, a reflection plate 412, a diffusion sheet 414, and apair of prism sheets 416.

The light emitting device 1 provides light. Here, the light emittingdevice 1 may be of a side view type. As described above, the lightemitting device 1 may be varied color temperatures of white light byadjusting the level of a driving bias. That is, the color temperaturesof white light emitted from the light emitting device 1 used for a BLUare varied, thereby creating image displays shown on an LCD panel 450 orproducing user's desired images.

The light guiding plate 410 serves to guide the light supplied to theLCD panel 450. The light guiding plate 410 may be formed of aplastic-based transparent panel such as acryl, and allows the lightgenerated from the light emitting device 1 to travel toward to the LCDpanel 450 disposed over the light guiding plate 410. Various patterns412 a for changing the traveling direction of the light incident intothe light guiding plate 410 to the LCD 450 can be printed on the rear ofthe light guiding plate 410.

The reflection plate 412 is provided on the rear surface of the lightguiding plate 410 and allows the light emitted in a downward directionto supply the light to the light guiding plate 410.

The reflection plate 412 reflects the light that is not reflected by thepatterns 412 formed on the rear surface of the light guiding plate 410toward an exit face of the light guiding plate 410, thereby reducingloss of light incident into the LCD panel 450 and enhancing uniformityof light transmitted to the exit face of the light guiding plate 410.

The diffusion sheet 414 diffuses incident light from the light guidingplate 410, thereby effectively preventing partial congestion of light.

The prism sheets 416 may include triangular prism patterns formed oneach surface in a predetermined arrangement. In an exemplary embodiment,the prism sheets may include two sheets including prisms alternatelyarranged at a predetermined angle to focus light diffused by thediffusion sheet 414 in a direction perpendicular to the LCD panel 450.

FIGS. 10 through 13 are diagrams illustrating light emitting systemsaccording to third through sixth embodiments of the present invention.

In detail, FIG. 10 illustrates a projector, FIG. 11 illustrates aheadlight of an automobile, FIG. 12 illustrates a street lamp, and FIG.13 illustrates an illumination lamp. The light emitting device 1 used inFIGS. 10 through 13 may be of a top view type.

Referring to FIG. 10, the light emitted from a light source 410 passesthrough a condensing lens 420, a color filter 430, and a sharping lens440, and is reflected at a digital micromirror device (DMD) 450. Then,the reflected light passes through a projection lens 480 to then reach ascreen 490. The light emitting device configured in accordance withembodiments of the present invention may be incorporated in the lightsource 410.

As in the projector shown in FIG. 10, in the automobile's headlightshown in FIG. 11, the street lamp shown in FIG. 12, and the illuminationlamp shown in FIG. 13, the color temperatures of white light emittedfrom the light emitting device 1 are varied by adjusting the level of adriving bias, thereby creating a variety of image displays.

While embodiments of the present invention has been particularly shownand described with reference to exemplary embodiments thereof, it willbe understood by those of ordinary skill in the art that various changesin form and detail may be made herein without departing from the spiritand scope of the present invention as defined by the following claims.It is therefore desired that the present embodiments be considered inall respects as illustrative and not restrictive, reference being madeto the appended claims rather than the foregoing description to indicatethe scope of the invention.

1. A light emitting device comprising: a light emitting element which isoperated by a forward driving bias to emit first light and includes afirst conductive layer of a first conductivity type, a second conductivelayer of a second conductivity type, a light emitting layer disposedbetween the first conductive layer and the second conductive layer, afirst electrode connected to the first conductive layer, and a secondelectrode connected to the second conductive layer, wherein the firstconductive layer, the second conductive layer and the light emittinglayer are represented by In_(x)Al_(y)Ga_((1-x-y))N (0≦x≦1, 0≦y≦1); and aphosphor layer including a phosphor which partially wavelength-convertsthe first light to emit second light, wherein the phosphor layerincludes only the phosphor or a combination of transparent resin and aphosphor, wherein if the light emitting element emits blue light, thephosphor layer includes a yellow phosphor which partiallywavelength-converts the blue light to emit yellow light and a redphosphor which partially wavelength-converts the blue light to emit redlight, or a green phosphor which partially wavelength-converts the bluelight to emit green light and a red phosphor which partiallywavelength-converts the blue light to emit red light, and wherein thelight emitting device emits white light using the first light and thesecond light such that a color temperature of the white light is variedby adjusting a level of the driving bias.
 2. The light emitting deviceof claim 1, wherein the phosphor is at least one selected from the groupconsisting of a nitride-/oxynitride-based phosphor, mainly activated bylanthanoids such as Eu and Ce; an alkaline earth halogen apatitephosphor, mainly activated by lanthanoids such as Eu or by transitionmetal elements such as Mn; an alkaline earth metal borate halogenphosphor; an alkaline earth metal aluminate phosphor; an alkaline earthsulfide phosphor; a rare earth aluminate phosphor, mainly activated bylanthanoids such as Ce; an alkaline earth silicate phosphor; an alkalineearth thiogallate phosphor; an alkaline earth silicon nitride phosphor;a germinate phosphor; a rare earth silicate phosphor; and an organic andan organic complexes, mainly activated by lanthanoids such as Eu.
 3. Thelight emitting device of claim 1, wherein the phosphor is at least oneselected from the group consisting of M₂Si₅N₈:Eu, MSi₇N₁₀:Eu,M_(1.8)Si₅O_(0.2)N₈:Eu, M_(0.9)Si₇O_(0.1)N₁₀:Eu (M represents at leastone element selected from among Sr, Ca, Ba, Mg and Zn), MSi₂O₂N₂:Eu,M₅(PO₄)₃X:R (X represents at least one element selected from among F,Cl, Br, and I, and R represents at least one element selected from amongEu and Mn), M₂B₅O₉X:R, SrAl₂O₄:R, Sr₄Al₁₄O₂₅:R, CaAl₂O₄:R,BaMg₂Al₁₆O₂₇:R, BaMg₂Al₁₆O₁₂:R, BaMgAl₁₀O₁₇:R, La₂O₂S:Eu, Y₂O₂S:Eu,Gd₂O₂S:Eu, YAG-based phosphors represented by Y₃Al₅O₁₂:Ce,(Y_(0.8)Gd_(0.2))₃Al₅O₁₂:Ce, Y₃(Al_(0.8)Ga_(0.2))₅O₁₂:Ce, and (Y, Gd)₃(Al, Ga)₅O₁₂, Tb₃Al₅O₁₂:Ce, Lu₃Al₅O₁₂:Ce in which portion or all of Y issubstituted with Tb or Lu, alkaline earth silicate phosphor,(SrBa)₂SiO₄:Eu, ZnS:Eu, and Zn₂GeO₄:Mn, MGa₂S₄:Eu (if necessary, thephosphor can contain at least one element selected from among Tb, Cu,Ag, Au, Cr, Nd, Dy, Co, Ni and Ti, in place of Eu, or in addition toEu).
 4. The light emitting device of claim 1, wherein the light emittingdevice is a package disposed within a slot of a package body, whereinthe slot is larger than the light emitting element, and the lightemitting element is placed in the middle of the slot, and wherein thepackage body is at least one selected from the group consisting of anorganic material having high light transmittance such as silicon resin,epoxy resin, acryl resin, glass resin, fluorine resin and imide resin,an inorganic material such as glass and silica gel, a variety of fillersincluding aluminum nitride, aluminum oxide, and composite materialsthereof, and a metallic or ceramic material.
 5. The light emittingdevice of claim 4, further comprising a transparent resin layer in theslot of the package body, wherein the transparent resin layer fillsapproximately 90% of the slot.
 6. The light emitting device of claim 5,wherein the transparent resin layer is formed of a material, filling theslot of the package body, which is at least one selected from the groupconsisting of epoxy resin, silicon resin, hardened silicon resin,denatured silicon resin, urethane resin, ocetane resin, acryl resin,polycarbonate resin and polyimide resin.
 7. The light emitting device ofclaim 1, wherein the driving bias is DC power.
 8. A light emittingsystem comprising: the light emitting device described in claim 1; and asensor which senses a user's body temperature, wherein the level of thedriving bias is controlled by the sensor.
 9. A light emitting systemcomprising the light emitting device described in claim 1.